I want to get drag force at the porous surface . I already got the pressure profile and velocity profile. I define the surface of the porous sphere as interior(B.C.).There is no relation theoritially between drag force and other parameters for porous sphere. If anyone know this kindly help me.

thanks for your kind reply. Actually I want to get the drag force for a porous sphere. If I define the bc of the porous as wall, then I can easily get the drag force, but for this case fluide not penetrate through the porous sphere. So I forced to define the porous sphere surface as interior and thats why I can't get grag force directly with respect to this interuior b.c. I get the following relation for drag force. You kindly write that how I have to proceed. I already get the pressure profile and vel. profile i.e. I know vel. and pr. at every points.

Calculation of the Drag Force :

A linear momentum balance on a control volume far away from the surface of the sphere yields the force on the body as a function of the change in momentum of the fluid passing through the control volume and the net pressure force on the control volume. For the net force in the ith direction, this momentum balance yields:

Fi = ¦A PdAi - ¦A r vi v.dA ----------(1)

Where, ¦ = sign on integration with respect to the elemental area A. r= density PdAi represent the component of the pressure force acting in the ith direction. The drag force is defined as the force acting opposite to the flow direction.